Hybrid vehicles are known for the reduction of emissions and fuel consumption. Their goal is to operate the internal combustion engine in the range of greatest efficiency, to turn off the internal combustion engine when the vehicle is idling, respectively traveling at low vehicular speeds, and electrically power it in these instances as well as using braking energy by means of recuperation. In the case of parallel hybrid engines, an addition of the torques from the internal combustion engine and one or more electric machines takes place. The electric machines are, for example, belt-driven starter generators or starter generators connected to the crankshaft of the internal combustion engine.
In modern internal combustion engines various operating points can be problematic with regard to exhaust gas emissions and fuel consumption. In the case of the gasoline engine, large torques, for example, require a deviation from the stoichiometric air-fuel mixture. A full load enrichment can likewise be necessary in order to keep component temperatures within acceptable limits. In order to set very small torques, a retardation of the ignition angle is common, which can also be deployed to achieve a lead torque, for example in order to make a rapid torque increase at idle possible. The degree of efficiency is, however, decreased by the shift in the ignition angle. In connection with overrun fuel cut-offs, increased nitrogen oxide emissions result on account of an oxygen surplus in the catalytic converter. Likewise when large torques are produced during the operation of a diesel engine, increased Bosch smoke degrees and nitrogen oxide emissions are too be anticipated. In the case of small torques, the danger exists that the catalytic converter cools down.
The German patent DE 10 2004 044 507, which was not pre-published, describes a method and a device to operate a motor vehicle drive with at least one internal combustion engine and with at least one electric machine, whereby the internal combustion engine and the electric machine produce a nominal required drive torque in a common manner. By means of a suitable deployment of the electric machine, unfavorable torque ranges and unfavorable, high alteration speeds of the optimal nominal torque of the internal combustion engine can be avoided.